Many industrial operations require heating materials to a high temperature in a furnace or equivalent apparatus. The requisite high temperature can be provided by combusting fuel with air, at a rate sufficient to provide heat of combustion that heats the materials. More recently, in operations termed “oxy-fuel”, the air as a source of oxygen is replaced by a gaseous feed containing more than 90 vol. % oxygen. Combustion with oxygen having such a high purity provides numerous advantages including attaining high temperatures, less diversion of heat to the non-reactive components of the feed air, and a lessened tendency to form nitrogen oxides.
One of the drawbacks of oxy-fuel melting is the higher operating cost. Using a gaseous feed stream with less than 90 vol. % oxygen as the oxidant, such as diluting a high purity oxygen from liquid supply stream with air, can reduce the unit cost of contained oxygen. However, using low purity oxygen reduces the energy efficiency of the oxy-fuel system, increasing the fuel consumption and, in turn, increasing the oxygen consumption, relative to the base case. Furthermore, if not properly managed, the resulting higher nitrogen content in the oxidant coupled with the high temperature flame can adversely impact NOx emissions from the process.
However, the present invention recognizes that when coupled with a heat recovery device such as a regenerator, even more advantages such as improved energy efficiency, reduced emissions, and improved furnace operation can be realized with operation using oxidant in which the oxygen content is less than what is used in oxy-fuel combustion.